Ethos is one of three modes of persuasion explained by Aristotle. It’s means “character” and serves as a measure of how credible one is when persuading an audience on the topic you are discussing--very important in rhetoric! According to Aristotle, there are three types of ethos: arête, phronesis, and eunoia.

I have spoken about arête before. It's the Greek word for "virtue," and in an ethical sense, it measn being the best version of yourself you can be. Aristotle believed that the ultimate goal in life for a human is happiness. In order to be fully happy in life, one would have to be virtuous. He describes the necessary steps to achieve this happiness in Nicomachean Ethics:

"[...] the man who is to be good must be well trained and habituated, and go on to spend his time in worthy occupations and neither willingly nor unwillingly do bad actions, and if this can be brought about if men live in accordance with a sort of reason and right order [...]" [Book x]

Phronesis is a Greek word for wisdom or intelligence. Aristotle didn't just mean to use it as an indication of IQ but also how well knowledge and skill are implemented in every day life. Someone with a low intelligence level can still be made wise by experience, for example. Aristotle believed that gaining phronesis required experience and there was no other wait to gain it.
Eunoia is Greek for “goodwill.” In rhetoric it is the relationship the reader cultivates with the audience to gain their trust. As a speaker, that trust is required to appear credible. Without it, you can't persuade an audience.

All three values--arête, phronesis, and eunoia--add up to create the meaning of ethos. According to Aristotle, ethos starts with good parenting, with teaching a child ethical behavior. Other teachers throughout life will add to this ethical framework. By learning skills we develop ourselves more, and also by exposing ourselves to many different experiences. By creating good habits and sticking with them until they become automatic, we develop each other even more. As a result, we will be happier, more productive people.